Gravimeter



thermal expansion and providing an easy and accurate process for measuring tempertures.

Referring more particularly to FIG. 1 which shows a diagrammatic section of the preferred embodiment of pyrometer of this invention, the pyrometer 1 comprises an elongated tubular member 3, within one end (righthand in FIG. 1) of which is provided a number of pyrolytic graphite disks stacked in a stack extending in the c-direction of the disks and this end portion is adapted to be exposed to the hot zone to be measured. The other end of the tubular member 3 is provided with a dial gauge 7 adapted to be responsive to a displacement of a detecting rod 2 owing to the thermal expansion of the cdirection stacked pyrolytic graphite disks. As described hereinbefore, the pyrometer 1 of this invention is characterized by the use of pyrolytic graphite as a thermally responsive element. In FIG. 1, a cap-like element 8 consists of a-direction pyrolytic graphite and the thermally responsive element 9 consists of the c-direction pyrolytic graphite. When the end of the tubular member 3 which consists of the c-direction pyrolytic graphite 9 housed in the cap-like a-direction pyrolytic graphite element 8 is exposed to the hot zone, it is seen that both the cap-like element -8 and the c-direction pyrolytic graphite 9* expand together owing to the high heat. At this time, the c-direction graphite 9 expand-s much more than the cap-like element 8, because the former has a larger coefficient of thermal expansion than the latter. Therefore, a graphite rod 2 accommodated within the tubular member 3 (this is made of graphite, too) is displaced by the difference of thermal expansion between the a-direction cap-like member 8 and the c-direction pyrolytic graphite 9 so that the dial gauge 7 moves its pointer in accordance with the displacement of the graphite rod 2.

Since the tubular member 3 of graphite and the graphite rod 2 housed therein are slidable with respect to each other, the displacement resulting from the difference in thermal expansion between the cap-like element 8 and the pyrolytic graphite 9* will be transmitted to a detecting means as a relative displacement between the tubular member 3 and the graphite rod 2. At the same time, the tubular member 3 serves as support which can be dipped into a hot zone to be measured.

In reference to the tubular member 3 and the rod 2, they are preferably made of graphite to obtain the benefits of refractoriness, and further, the outside of the tubular member 3 is preferably coated with a heat resisting coating material, such as, silicon carbide and the like, in order to enhance its refractoriness. In addition, the tubular member 3 and the graphite rod 2 are preferably made of a graphite material of the same quality or having the same coefficient of thermal expansion so as not to affect the displacement owing to thermal expansion of the thermally responsive element 9.

As shown in FIG. 1, the cap-like element '8 is fixed to the right end of the tubular member 3 by machining or shaping the end portion thereof. It is to be noted that the cap-like element 8 is secured to the tubular member 3. A number of pyrolytic graphite disks 9 which expand most in the c-direction are inserted within the cap-like element 8 in such manner that the planes of deposition thereof are perpendicular to the axis of the tubular member 3.

A disk of pyrolytic graphite 9 can be made as thick as desired by the technique of deposition, but it has been found that the larger the number of disks of graphite forming the element 9 the more accurate it will be. In connection with the thickness of pyrolytic graphite element 9, FIG. 7 shows the graphical diagrams of the results of experimental research conducted on the displacement due to thermal expansion of a stack of disks which are 9.8 mm., 19.7 mm., 30.0 mm., 39.6 mm., 51.0 mm., 60.0 mm., and 82.7 mm. in thickness respectively, and which form the pyrolytic graphite laminated assembly.

As shown in FIG. 1, the graphite rod 2 is slidably provided within the tubular member 3 in contact with the laminated pyrolytic graphite element 9, and a detecting terminal 5 is provided on a fixture 4. A coil spring 6 is provided around the terminal 5 so as to urge it towards the rod 2. The terminal 5 is connected to a direct reading type dial gauge 7 to complete the pyrometer of this invention.

It is understood that this pyrometer can be combined with a temperature calibrated instrument by the aid of a known differential transformer in order to let it record the course of temperature measurement automatically. Another preferred embodiment of the pyrometer combined with the automatic record means is shown in FIG. 3, which will be described hereinafter.

One feature of the thermally responsive element consisting of pyrolytic graphite of this invention lies in the fact that the sensibility of temperature measurement of this pyrometer depends upon the thickness of the element. For example, it has been found that when the element is 10 mm. in thickness, it expands 3 micron per 10 C. while it is 20mm. it expands 3 micron per 5 C.

In order that the pyrometer of this invention can be used effectively, it is preferred that a standard temperature graph should be initially made and used as a standard for correcting the temperature scale of the pyrometer. Once corrected, it is no longer required to correct it again.

In the pyrometer of FIG. 1, the pyrolytic graphite of cap-like element 8 is oriented so that the expansion in the a-direction is parallel to the length of the pyrometer, while the graphite of the disks 9' is oriented so that the expansion in the c-direction is parallel to the length of the pyrometer. Therefore the graphite of disks 9 expands more than that of cap-like element 8 to transmit displacement resulting from expansion to the rod 2, whereby the pointer of the dial gauge 7 is moved thereby to indicate temperature. However, theoretically it is understood that the above arrangement of graphites of members 8 and 9' should be such that the expansion of one is in the adirection and that in the other in the c-direction for temperature measurement. When the graphites of members 8 and 9 are arranged in this relationship, it follows that the pointer of the dial gauge 7 indicates the difference in the expansion. However, it is expedient to have the elements 8 and 9 arranged as in FIG. 1 from the viewpoint of manufacture. As described hereinbefore, the pyrolytic graphite 9 may be in the form of a number of flat disks or a single block.

The pyrometer of this invention shown in FIG. 1 has a range of temperature measurement in which the pyrolytic graphite 9 exhibits a uniform thermal expansion. When the pyrolytic graphite deposited at a temperature of 2100 C. is employed, it is preferred that the range of measurement should be from room temperature to 2300 0, because it has been found that there is a fluctuation of size at a temperature of 2400 C. and upwards. However, it has been discovered that pyrolytic graphite deposited at 2100 C. and then subjected to heat treatment at a much higher temperature, say, 3000 C. and upwards, can be employed as a thermally responsive element up to the temperature of heat treatment. Experimentally, it has been found that the range of temperature measurement of the pyrometer consisting of pyrolytic graphite heat treated at 3500 C. is from room temperature to 3500 C.

Referring more particularly to the pyrometer of FIG. 1, the tubular member 3 and the graphite rod 2 are made of the same material having the same coefficient of thermal expansion, hence they expand similarly as they are heated so that their thermal expansion will not be detected. However, since the graphites of elements 9 and 8 have their respective different coefficient of thermal expansion, the difference of thermal expansion will be United States Patent 3,498,134 GRAVIMETER Jury Dmitrievich Bulanzhe, Ul. Dmitria Ulianova 4/ 34, korpus B, kv. 64; and Valentin Antonovich Romanjuk, Ul. Vavilova 37-2, kv. 46, both of Moscow, U.S.S.R.; and Sergei Alexeevich Poddnbny, Ul. Mal. Podyacheskaya 6, kv. 18, Leningrad, U.S.S.R.

Filed Aug. 17, 1967, Ser. No. 661,427 Int. Cl. G01m 1/12 US. Cl. 73--382 3 Claims ABSTRACT OF THE. DISCLOSURE A gravimeter having a resilient system which comprises a pendulum sensitive togravitation acceleration and mounted on a rotary frame in such a manner that the axis of'rotation oftlie pendulum is perpendicular to the axis of rotation of the rotary frame, thus providing for practically an unlimited range of measurements. The

pendulumof the resilient system may be astatized to ensure an-increased precision of measurements.

The present invention relates to the field of gravimetry and, more particularly to gravimeters designed for measuring on the ground great differences in gravitational acceleration when creating reference gravimetric networks. I

There are known gravimeters consisting of a rotary frame with a resilient system installed thereon and a device for measuring the turn angle of the frame.

The resilient system of said gravimeters is installed so that the axis of rotation of a pendulum of the resilient system is parallel to the axis of rotation of the rotary frame. The value of gravitational acceleration is calculated by the value of the turn angle of the frame. 7

The disadvantages of said gravimeters are as follows: low accuracyof measurements, different sensitivity of the resilient system 'when tilted above or below the horizon, a necessity to calibrate the device intended for measuring the turn angle of the frame, impossibility to employ an astatized resilient system.

An object of the present invention is to develop a widerange high-accuracy gravimeter.

Another object of the invention is to develop a gravimeter which does not require calibration of the device intended for measuring the turn angle of the frame.

In acocrdance with said and other objects in the gravimeter, according to the invention, the axis of rotation of the pendulum of the resilient system is normal to the axis of rotation of the rotary frame.

Other objects and advantages of the present invention will become apparent hereinbelow upon considering the description of its exemplary embodiment and the accompanying drawings, wherein a general axonometric view of the gravimeter of the invention is shown, partly in section.

The gravimeter consists of a rotary frame 1 'with a resilient system 2 rigidly mounted thereon. The resilient system 2 is accommodated in a thermostat (not shown in the drawing) and incorporates a pendulum 3 with an axis of rotation 4 'which is normal to the axis of rotation 5 of the rotary frame 1, a spring 6 for astatizing the resilient system 2, a range unit 7, a damping unit which is essentially a plate 8, a lighting means 9 and a device for observing the position of an index of the pendulum 3 and constituted as a microscope 10. The pendulum 3 is placed in a vacuum chamber (not shown in the drawing).

The resilient system need not be astatized, while the damping unit of the pendulum 3 may be of an air, liquid or electromagnet type.

The position of the pendulum 3 may be also determined by means of electrical indication. In this case, an electric signal depending on the position of the pendulum 3 may 'be obtained from a photocell in which the light reflected from the pendulum 3 is converted into an electric signal or by means of a capacity transmitter.

The device intended for measuring the turn angle of the rotary frame 1 in the gravimeter of the invention comprises a limb 11 graduated in degrees and coupled with the frame 1 and a unit 12 adapted for taking readings from the limb 11 and mounted on a base 13.

Such a design of the gravimeter proposed herein makes it unnecessary to calibrate the device intended for measuring the turn angle of the rotary frame 1 of the gravimeter and to obtain the results of measurements in units of the C.G.S. system.

However, the turn angle of the frame 1 of the gravimeter, according to the invention, can be measured in linear measuring units, but in this case, the device intended for measuring the turn angle of the rotary frame 1 should be calibrated.

Observations with the aid of the gravimeter of the invention can be accomplished as follows.

The gravimeter should be installed in the point of observation and levelled. The frame 1 should be uncaged and, by turning a differential screw 14, tilted below the horizon until the pendulum 3 assumes a strictly fixed position relative to the frame 1 (zero position). The position of the pendulum 3 should be observed with the help of the microscope 10. With the pendulum 3 set to the zero position, readings should be taken from the limb 11.

Further the frame 1 by turning the screw 14 is tilted above the horizon until the pendulum 3 assumes a zero position and then readings should be taken from the where ,8 is the angle of tilt of the axis of rotation 4 of the pendulum 3 of the resilient system relative to the horizon;

g is the gravitational acceleration at the point of observation The value g may be varied by changing the tilt of the axis of rotation 4 of the pendulum 3 of the resilient system 2. At a certain g equalling g the pendulum 3 assumes a strictly definite position with respect to the frame 1 (zero position). This position is determined with the aid of the microscope 10. There are two angles [3 at which g'=g having designated them as p and ,8", we obtain g =g cos B=g cos 3":g cos B (2) i.e. fi=;8'= 8" (tilt above and below the horizon).

Angle ,8 is equal to half of the total turn angle of the frame 1. The value (1) can be presented as follows:

-y.( fi- )=9g. where the readings of the gravimeter are,

r= o fi (4) 1 1 by means of the differential transformer 13 to record temperature measurement in an automatic manner. ,The function of the differential transformer has been described hereinbefore.

In addition, the above pyrometer was dipped into the molten iron tapped from a blast furnace for measuring the temperature of molten iron. In this case, one end including the thermally responsive element of the pyrometer was dipped into the molten iron to the depth of 90 mm. in order to effect an automatic recording of temperature. The temperature of the molten iron has hardly ever been measured in a continuous manner in the past. However, it has been measured continuously for a period of about 90 minutes by the automatic recording means combined with the pyrometer of this invention. The temperatures measured were l3401460 C. In addition, it has been found that the surface of the cap-like element of pyrolytic graphite was not corroded by the molten iron nor did slag adhere to it.

As many changes could be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings, shall be interpreted as illustrative and not in a limiting sense.

We claim:

1. A pyrometer comprising a thermally responsive means, an intermediate means and a temperature indicating means, said thermally responsive means comprising two members made of anisotropic graphite material having an anistoropy of thermal expansion in two directions which are perpendicular to eachot'her, said one member of said thermally responsive means being a cap-like member the graphite material of which is oriented with the lower coefiicient of expansion in a direction parallel to an axis of said pyrometer, and said other member being a plurality of graphite disks in said cap-like member and stacked in the direction parallel to said axis of said pyrometer and with the material oriented with the higher coefficient of expansion in the stacking direction, said intermediate member comprising a tubular member with said cap-like member thereon and a rod member both of which members are of a refractory material having the same coeflicient of expansion, said rod member being engaged with said disks and slidable within said tubular member with the thermal expansion of said disks, and said temperature indicating means being engaged with said rod member and tubular member and having a pointer indicating a temperature in responose to the difference of thermal expansion between said two members of said thermally responsive means.

2. A pyrometer as claimed in claim 1 in which said anisotropic graphite material is a material selected from the group consisting of pyrolytic graphite, natural graphite, and recrystallized graphite.

3. A pyrometer as claimed in claim 2 in which said graphite is pyrolitic graphite deposited at a temperature of l6002500 C.

4. A pyrometer as claimed in claim 2 in which said graphite is pyrolytic graphite heat treated at a temperature of 20003600 C.

5. A pyrometer as claimed in claim 2 in which said graphite is pyrolytic graphite containing 0.0l3% by weight of an element selected from the group consisting of boron, molybdenum, silicon and bromine.

6. A pyrometer as claimed in claim 1 said plurality of graphite disks are laminated to one another and positioned within the end of said cap-like member.

7. A pyrometer as claimed-in claim 1 in which said refractory material of said tubular member and said rod is a material selected from the group consisting of artificial graphite, pyrolytic graphite, recrystallized graphite, natural graphite, tungsten, rhenium, tantalum, ZrO 'ThO MgO, HfO CeO CaO, BeO-ZrO ThO -ZrO HfC, MoC, NbC, TaC, ThC, TiC, VC, WC, ZrC, and BN.

8. A pyrometer as claimed in claim 1 in which said cap-like member and said tubular member are of the same refractory material.

9. A pyrometer as claimed in claim 1 in which said tubular member and said cap-like member are coated with silicon carbide.

References Cited UNITED STATES PATENTS 3,038,337 6/1962 Diefendorf 73363.9 x

FOREIGN PATENTS 250,021 1929 Italy.

286,002 7/1914 Germany.

LOUIS R. PRINCE, Primary Examiner JOSEPH W. ROSKOS, Assistant Examiner 

